Impregnation of porous gels with a solid material



Patented Dec. 10, 1929 UNITED STATES. PATENT OFFICE HARRY N. HOLMES, OI OBERLIN, OHIO IIIPBEGNA'IION OI POROUS GELS WITH A. SOLID MATERIAL No Drawing.

This invention relates to a method of depositing coatings of solid material, such as oxides,.hydroxides, sulfides, or the like, in porous solids. The invention has for its object to provide a method by which the solid material is deposited, uniforml throughout all cavities and pores, with the a ility to read-' ily free the porous material from all traces of undesirable material, such as soluble salts, 1 and to insure penetration of the material to be deposited throughout the lump or mass of porous material.

In the broad sense the invention contemplates the deposition of the solid material by the reaction between two substances which under certain conditions do not react with each other and under other conditions do react with each other, by first distributing or diffusing the two substances through the pores of the porous solid under the first conditions, followed by a change to the second condition with accompanying reaction and deposition. Several instances of such substances and conditions will be apparent to chemists. One thereof, forming the subject matter of my oo-pending application for Impregnation of porous gels with metals or other insoluble material, filed of even date herewith, Ser.No. 212,828, utilizes two substances, such as formalin solution and slightly basic chloro-platinic acid which do not react appreciably at room temperature or lower but will precipitate metallic platinum at about 100 C. The 'changein conditions here is the chem e in temperature and the two substances, eit er separately or otherwise, are

- distributed through the porous solid at a low temperature and with the substances in situ reaction occurs when the temperature is raised- Further details of this method will Application fled new 13, 1927. Serial. 1%. 212,828.

othei' substance, such as a gas, in solution, for

the deposition of desirable material, by first introducing the soluble salt into the pores as a solution, ringing the reacting gas into contact with the salt under conditions in which reactim cannot occur, and subsequently producing solution and reaction by the introduction of a suitable pore penetrating solvent liquid, such as water. This method avoids the non-penetrating surface effect which usually results when a porous material soaked with a solution of one reagent is subjected to the eiiect of a second rea ent, thereby producing deposition in the surface pores and clogging or choking the porous material, so that the precipitatm reaction does not continue to the center, of the lumps or masses.

The invention is capable of use for the deposition of numerous solid materials in porous solids under the conditions described, but certain specific reactions will be presented in detail for more complete understanding of the invention. 7

The porous solid may be of any suitable form provided with either or both of mlcroscopic or ultra-microscopic pores, such as a silica gel, and, for example, may be the slhca gel described in my prior application Ser. No. 56,077, filed Se tember 12, 1925, or m the application fil 'ointly by m self and John A. Anderson, Ser. No. 656, 16, filed August 10, 1923. Such a silica gel is crushed or otherwise reduced to fragments of suitable size, say to half the size of a grain of wheat, and 1s soaked with a water-solut1on of a suitable metallic salt, such as a molar solution of ferric chloride, the soaking being permitted to continue for a few minutes at room' temperature. Solutions of other concentrations than that specified are also sultable. Diffusion or penetration of the solution through and into the Force is rapid and complete in a short time. he fra ents are 'then dried so that the dried soli ,--in this carried mat a temperature slightly above 100 C. until practically all of the water is driven off. The solid is now cooled to room temperature or lower and a stream of a suitable gas, in this case dry ammonia gas or air containing the same as, is passed over or through the gel unti adsorption is practically complete The first step with the ferric chloride has left a film of solid reacting material uniformly deposited by encrustation on the walls or in a fraction of the free space of every ore, but obviously v without materially distur ing interpore communication. When the gas is passed over the gel it also difiuses rapidly and complete 1y throu hout all of the now encrusted pores or cham ers.

The gel is now moistened with water in quantity somewhat more than sufiicient to solution containing ammonium chloride.

The wetporous solid is now drained and is washed in repeated changes of pure water, preferably heated, until the washings are ree from soluble salts, although in some cases washing, or at least complete washing, is not essential. The impregnated el is now dried in any desired manner, again taking care not to injure either the deposited material or the gel structure, such as by not allowing the temperature to exceed say'600 C. The ferric oxide is thus uniformly distributed throughout the gel without completely clogging the capillaries, with the ability to catalytically aid reaction of mixtures of ases which can thereby be brought into exce lent contact with the greatly extended surface of tation, as before.

more metallic salts, followed b dif- 3 i the active ferric oxide in the gel.

It is also possible to secure a deposit of mixed oxides by initially impregnating the gel with a mixture of solutions of two or fusion of the reacting gas into t e ca rice, and the introduction of water or 0t er suitable liquid to produce solution and precipi- Silver sulphide may be deposited uniform ly throu hout the porous so (1 by first soaking the ry gel in a silver nitrate solution of sultable strength, such as molar stren h, then drying, heating to approximately 1 coolin allowing dry hy rogen sulphlde gas to di use throughout, say to the point of saturation, and then moistening with sufiicient water to dissolve both the salt and the hydrogen sulphide gas to permit their immediate reaction. he recipitate may be washed or not, as desired? 7 takes place.

What I claim is:

1. The method of impregnating a dry rigid-walled porous gel containing microscopic and ultar-microscopic pores with catalytic material, consisting in causing two substances which under certain conditions react upon each other to form catalytic material but which under other conditionsdo not materially react with each other to become uni formly distributed or diffused through the pores under said other conditions, and then with said substances in situ subjecting the porous solid to said first named condition under which reaction between said substances will occur, thereby depositing solid catalytic material in substantially all of the pores of the porous gel.

2. The method of impregnating a dry rigid-walled porous gel containing miscrescopic .and ultra-microscopic pores with catalytic material, consisting in introducing into substantially all of the capillaries of the porous solid a soluble substance and a soluble gas capable of reacting therewith to precipitate the desired catalytic material, and then causing dilfusion through the ca illaries of a solvent in which the precipitatmg reaction 3.The method of impregnating a dry rigid-walled porous gel containing microscopic and .ultra-microscopic pores with catalytic material, consisting in causing diifusion through substantially all of the capillaries of a solution of a substance adapted to react with a solution of a suitable gas to form the desired catalytic material, dryi 1g, causing said gas to diffuse through the cap' laries, and introducing'into the capillaries a solvent for both said gas and reacting substance, to thereby produce deposition in substantially all of the capillaries of the desired catalytic material.

4. The method of impregnating a dry rigid-walled porous gel containing microscopic and ultra-microscopic pores with catalytic material, consisting in causing diffusion through substantially all of the ca illaries of a solution of a substance adapte to react with a solution of a suitable gas to form the desired catalytic material, drying causing said gas to difiuse through the capillaries, and introducing into the capillaries a solvent for both said gas and reacting substance, to thereby produce deposition in substantiall all of the capillaries of the desired materia washing out excess soluble reacting substance, 7

and d ing.

5. T e method of impregnating a dry rigid-walled porous gel containing micro scopic and ultra-micropscopic pores with catalytic material consisting 1n separately introducin into substantially all of the capillaries a ried deposit of a solid substance and also a gas capable of reactin with a solution of the solid substance to prod uce a deposit of catalytic material, and causing diffusion throu bout the capillaries of a solvent for said geposit and gas and forming the desired material in substantially all of the capillaries. In testimony whereof I hereby aflix my signature.

HARRY N. HOLMES. 

